In a known way, the samples are examined by specialized and trained observers for detecting cells which may be pathological in a sample positioned on an analysis plate or slide. In order to allow the detection of potentially pathological cells, the sample undergoes a treatment, such as staining with which it is possible to show i.e. the characteristics of the nucleus and the cytoplasm of the cells in order to assist with locating and diagnosing pathological cells. When the sample is observed, the potentially pathological cells then show differences in tinctorial affinities, in size and shape, both at the nucleus and at the cytoplasm with respect to normal cells.
The analysis may be accomplished manually, without any particular assistance. In this case, the physician or specialized technician scrolls through the sample plates under a microscope and observes each of them with view to detecting morphological abnormalities indicating pathological cells which may correspond to a precancer or cancer condition for example. Such an analysis method is tedious and is considerably time-consuming. Further, it does not provide any satisfactory results especially with a number of “false negatives” estimated to be about 30%, i.e. of samples considered as normal while there exists a pathology in the patient, notably a precancer or cancer pathology with the risks of subsequent development of cancer in a wrongly reassured patient.
In order to improve the results of the analysis, it was proposed to improve the sampling, i.e. the number of cells, their fixation, their staining and their spreading out on the analysis plate, but also to assist the physician or specialized technician in his/her analysis, for example by computer analysis means, such as image processing software and other means.
For this purpose, a camera or a still camera is used for acquiring images of the different areas of the sample positioned on the analysis plate and transmitting the data of these images to a computer system which then operates on a <<virtual>> analysis plate.
This computer system allows processing of the signal, pre-processing of the images and a comparative analysis of the images with optionally newly generated or existing databases in order to accelerate the analysis process, and thereby allow a larger number of samples to be analysed and to assist the physician or specialized technician. The images of a sample are for example examined automatically and, if certain areas having an abnormality are recorded, the corresponding images are passed on to a physician or specialized technician who may then determine whether these areas show pathological cells or not. The physician or specialized technician therefore observes nothing more than abnormal areas without analyzing the areas considered as normal by the computer system. Such a method actually allows an acceleration of the analysis and makes the diagnosis more reliable.
However, the physician or specialized technician then no longer has the opportunity of observing normal samples or samples having minor morphological changes, which is detrimental to his/her appreciation of the samples and especially to his/her learning curve or even to the preservation of his/her diagnostic acuity. Indeed, the analysis of samples is based on the training and practice of the physician or specialized technician in examining samples and in comparing normal areas and areas having abnormalities. The fact of suppressing this practice by a computer-aided analysis may lead physicians or specialized technicians to lose their skills and thereby causing errors in analysis.
Further, contrary to the field-by-field scanning the line-by-line scanning of a color image requires the deletion or Red/Green/Blue (RGB) registration which needs a high level of adjustment for the alignment of the images, this high adjustment level being sensitive to the slightest vibrations. Consequently, this line-by-line scanning for a color image may take a long time because of the processing operations applied on the slide during the scanning. Further, the scanning of a color image requires significant image compression times.
Moreover, the scanning is delicate for samples containing three-dimensional clusters of cells, i.e. <<stacks of cells>>, notably of pathological cells. Indeed, the focusing by the camera is accomplished at a thickness of the cluster defined by one or more focal points at the cluster, leaving the other deeper or more superficial points in the fuzziness. In order to obtain a proper <<large field>> image, i.e. of the entirety of the analysis plate, for a screening or diagnostic read-out on the single virtual plate, it is required to have a “blurred” surface as small as possible (less than 5%). Further, the segmentation tools are more difficult to handle on blurred areas affecting both the isolated cells and the three-dimensional clusters. Consequently, the analysis of the cells and the nuclei becomes much less relevant and may even cause poor categorization of the cells.
The invention aims at overcoming the drawbacks mentioned above by proposing an analysis method which, while allowing time to be saved in the scanning processes, makes it more performing in terms of surface that can be analysed, and more performing in terms of quality of detection of cell abnormalities for computer aided analysis, within the scope of a more relevant quality control associating diagnostic check points and diagnosis training points for the physician or specialized technician.